A method of operating a laundry washing machine comprising a recirculation circuit

ABSTRACT

A method for operating a laundry washing machine comprising a washing tub external to a washing drum, a recirculation system comprising a recirculation circuit configured to drain liquid from the bottom of the washing tub and to re-admit such liquid into the washing tub, a liquid level sensor device configured to detect the liquid level inside the washing tub, and a variable speed recirculation pump connected to the recirculation circuit. The method comprises a recirculation phase comprising controlling the recirculation pump by varying the rotation speed of the recirculation pump depending on a difference between the detected liquid level and a prefixed liquid level value.

The present invention concerns the field of laundry washing techniques.

Specifically, the invention relates to a method for controlling a laundry washing machine equipped with a recirculation circuit.

BACKGROUND ART

Nowadays the use of laundry washing machines, both “simple” laundry washing machines (i.e. laundry washing machines which can only wash and rinse laundry) and laundry washing-drying machines (i.e. laundry washing machines which can also dry laundry), is widespread.

In the present description, therefore, the term “laundry washing machine” will refer to both a simple laundry washing machine and a laundry washing-drying machine.

Laundry washing machines generally comprise an external casing, or cabinet, provided with a washing tub which contains a rotatable perforated washing drum where the laundry is placed. A loading/unloading door ensures access to the washing drum.

Laundry washing machines typically comprise a water supply unit and a treating agents dispenser, preferably equipped with a drawer, for the introduction of water and washing/rinsing products (i.e. detergent, softener, rinse conditioner, etc.) into the washing tub.

Known laundry washing machines are typically provided with a water outlet circuit suitable for withdrawing liquid, for example dirty water, from the bottom of the washing tub to the outside. The water outlet circuit is typically provided with a controllable draining pump.

Known laundry washing machines are also typically provided with one or more recirculation circuits.

A known recirculation circuit which equips laundry washing machines is adapted to drain liquid from the bottom region of the washing tub and to re-admit such a liquid into an upper region of the washing tub. The recirculation circuit is preferably provided with a terminal nozzle opportunely arranged so that the recirculated liquid is conveyed over the laundry and distribution of the same liquid over the laundry is enhanced. The recirculation circuit is typically provided with a recirculation pump.

During the washing cycle, the recirculation pump is opportunely activated at proper times to recirculate liquid from the bottom of the washing tub and to convey it over the laundry.

This recirculation phase is preferably carried out at the beginning of a washing cycle when the laundry needs to be completely soaked. Furthermore, this action is preferably carried out during rinsing phases at the beginning of the washing cycle and/or during rinsing phases in successive steps of the washing cycle, for example rinsing phases following the main washing phase.

The aim of a recirculation phase is generally to improve wetting of the laundry received in the washing drum, preferably either at the beginning of the washing cycle before the main washing phase with use of detergent or in any rinsing phase of the washing cycle.

According to a preferred embodiment of the known technique, the recirculation phase is carried out by operating the recirculation pump at a prefixed speed for a prefixed/estimated period of time.

The recirculation pump is then deactivated when said period of time elapses.

Furthermore, the recirculation pump may be deactivated within said period of time if the liquid level inside the washing tub goes below a minimum threshold value, for example a minimum threshold value set above the pump inlet in order to avoid suction cavitation.

An aim of the present invention is to improve wetting of laundry during a recirculation phase compared to known techniques.

Another aim of the present invention is to accelerate wetting of laundry during a recirculation phase compared to known techniques.

It is a further aim of the invention the optimization of the recirculation of the washing liquid and the laundry wetting assuring the necessary water level inside the washing tub.

It is another aim of the invention the optimization of the recirculation of the washing liquid flow in function of its actual quantity collected inside the washing tub.

DISCLOSURE OF INVENTION

Applicant has found that by providing a laundry washing machine comprising a washing tub external to a washing drum and a recirculation system comprising a first duct terminating at a first region of the washing tub and by providing a variable speed recirculation pump operable at a speed depending to the detected liquid level inside the washing tub, it is possible to reach the mentioned objects.

In a first aspect thereof the present invention relates, therefore, to a method for operating a laundry washing machine comprising:

-   -   a washing tub external to a washing drum suited to receive the         laundry to be washed;     -   a water supply system suitable to convey water to said washing         tub;     -   a recirculation system comprising a recirculation circuit apt to         drain liquid from the bottom of said washing tub and to re-admit         such liquid into a first region of said washing tub, said         recirculation system comprising a variable speed recirculation         pump having an outlet connected to said recirculation circuit         and wherein said recirculation pump is operable at variable         speeds to circulate liquid through said recirculation circuit;     -   a liquid level sensor device suited to detect the liquid level         inside said washing tub;     -   the method comprising a recirculation phase to drain liquid from         said bottom of said washing tub and to re-admit such liquid into         said first region of said washing tub through said recirculation         circuit, wherein said recirculation phase comprises the step of         controlling said recirculation pump by varying the rotation         speed of said recirculation pump depending to the difference         between the detected liquid level and a prefixed liquid level         value.

Preferably, the method comprises a step of activating the recirculation pump when the detected liquid level is above the prefixed liquid level value.

Preferably, the method comprises a step of deactivating the recirculation pump when the detected liquid level is equal to, or goes below to, the prefixed liquid level value.

In a preferred embodiment of the invention, the rotation speed of the recirculation pump is directly proportional to the difference between the detected liquid level and the prefixed liquid level value.

According to a preferred embodiment of the invention, the rotation speed of the recirculation pump is comprised between a minimum threshold value and a maximum threshold value.

In a preferred embodiment of the invention, the minimum threshold value is zero.

In a further preferred embodiment of the invention, the minimum threshold value is greater than zero.

According to a preferred embodiment of the invention, the rotation speed of the recirculation pump is varied over the time according to a continuous function or a step function.

In a preferred embodiment of the invention, the method further comprises a step of reestablishing the prefixed liquid level value inside the washing tub when the liquid level goes below the prefixed liquid level value by conveying an amount of water into the washing tub.

Preferably, said amount of water is supplied into the washing tub through the water supply system.

In a further preferred embodiment of the invention, the method further comprises a step of reestablishing the prefixed liquid level value inside the washing tub when the liquid level goes below the prefixed liquid level value by extracting an amount of water from the laundry in a dewatering process carried out by rotating the washing drum at a dewatering speed.

Preferably, at said dewatering speed laundry stuck to the inner side wall of the washing drum

In a preferred embodiment of the invention, the recirculation system comprises a second recirculation circuit apt to drain liquid from the bottom of the washing tub and to re-admit such liquid into a second region of the washing tub, wherein the variable speed recirculation pump is a bi-directional variable speed pump having a second outlet connected to the second recirculation circuit, said recirculation phase being performed activating said recirculation pump in a first direction of rotation, and wherein the method comprises a further recirculation phase to drain liquid from the bottom of the washing tub and to re-admit such liquid into the second region of the washing tub through the second recirculation circuit, wherein the further recirculation phase comprises the step of activating the recirculation pump in a second direction of rotation opposite the first direction of rotation.

According to a preferred embodiment of the invention, the recirculation pump is operated in the second direction at a first fixed speed.

According to a further preferred embodiment of the invention, the recirculation pump is operated in the second direction at a speed varying over the time.

In a further preferred embodiment of the invention, the recirculation system comprises a second recirculation circuit apt to drain liquid from the bottom of the washing tub and to re-admit such liquid into a second region of the washing tub, wherein the outlet conveys liquid to a bifurcation for the recirculation circuit and the second recirculation circuit, wherein the recirculation circuits are configured so that a liquid in the second recirculation circuit requires a pressure to reach the washing tub which is lower than the pressure required for a liquid in the recirculation circuit to reach the washing tub, and wherein the recirculation pump is operated at a first speed below, or equal to, a speed threshold to circulate liquid only in the second recirculation circuit to reach the washing tub and the recirculation pump is operated at a second speed above the speed threshold to circulate liquid both in the first recirculation circuit and the second recirculation circuit to reach the washing tub, wherein the step of controlling the recirculation pump by varying the rotation speed of the recirculation pump depending to the difference between the detected liquid level and the prefixed liquid level value is carried out when the recirculation pump is operated above the speed threshold.

According to a preferred embodiment of the invention, the recirculation pump is operated at a first speed to circulate liquid only in the second recirculation circuit to reach a bottom region of the washing tub and is operated at the second speed to circulate liquid also in the first recirculation circuit to reach an upper region of the washing tub.

Preferably, the first region of the washing tub is an upper region of the washing tub.

Preferably, the second region of the washing tub is a bottom region of the washing tub.

BRIEF DESCRIPTION OF THE DRAWINGS

Further characteristics and advantages of the present invention will be highlighted in greater detail in the following detailed description of some of its preferred embodiments, provided with reference to the enclosed drawings. In the drawings, corresponding characteristics and/or components are identified by the same reference numbers. In particular:

FIG. 1 shows a perspective view of a laundry washing machine where a method according to a first preferred embodiment of the invention is implemented;

FIG. 2 shows a schematic view of the laundry washing machine of FIG. 1;

FIG. 3 shows a schematic view of a laundry washing machine according to a second preferred embodiment of the invention;

FIG. 4 shows a perspective view of a laundry washing machine according to the second preferred embodiment of the invention with some external casing sides removed therefrom;

FIG. 5 shows some elements of FIG. 4 isolated from the rest;

FIG. 6 shows an element of FIG. 5 isolated from the rest;

FIG. 7 is a plan view from above of the element of FIG. 6;

FIG. 8 is a plan sectional view taken along line VIII°-VIII° of FIG. 7;

FIG. 9 shows a detail of a further embodiment of FIG. 4;

FIG. 10 shows some elements of FIG. 9 isolated from the rest;

FIG. 11 shows an element of FIG. 10 isolated from the rest;

FIG. 12 is a plan view from above of the element of FIG. 11;

FIG. 13 is a plan sectional view taken along line XIII°-XIII° of FIG. 12;

FIG. 14 shows a detail of a further embodiment of FIG. 4;

FIG. 15 shows some elements of FIG. 14 isolated from the rest;

FIG. 16 shows an element of FIG. 15 isolated from the rest;

FIG. 17 is a plan view from above of the element of FIG. 16;

FIG. 18 is a plan sectional view taken along line XVIII°-XVIII° of FIG. 17;

FIG. 19 shows a further embodiment of FIG. 4;

FIG. 20 shows some elements of FIG. 19 isolated from the rest;

FIG. 21 shows some elements of FIG. 20 isolated from the rest;

FIG. 22 shows some elements of FIG. 21 isolated from the rest;

FIG. 23 shows a partial sectional view of FIG. 22.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

The present invention has proved to be particularly advantageous when applied to laundry washing machines, as described below. It should in any case be underlined that the present invention is not limited to laundry washing machines. On the contrary, the present invention can be conveniently applied to laundry washing-drying machines (i.e. laundry washing machines which can also dry laundry).

With reference to FIGS. 1 and 2 a preferred embodiment of a laundry washing machine 1 in which a method according to a preferred embodiment of the invention is implemented is shown.

The laundry washing machine 1 preferably comprises an external casing or cabinet 2, a washing tub 3, a container 4, preferably a perforated washing drum 4, where the laundry to be treated can be loaded.

The washing tub 3 and the washing drum 4 both preferably have a substantially cylindrical shape.

The washing tub 3 is preferably connected to the cabinet 2 by means of an elastic bellows, not shown. The bellows is preferably S-shaped.

The cabinet 2 is provided with a loading/unloading door 8 which allows access to the washing drum 4.

The washing drum 4 is advantageously rotated by an electric motor, not illustrated, which preferably transmits the rotating motion to the shaft of the washing drum 4, advantageously by means of a belt/pulley system. In a different embodiment of the invention, the motor can be directly associated with the shaft of the washing drum 4.

The washing drum 4 is advantageously provided with holes which allow the liquid flowing therethrough. Said holes are typically and preferably homogeneously distributed on the cylindrical side wall of the washing drum 4.

The bottom region 3 a of the washing tub 3 preferably comprises a seat 15, or sump, suitable for receiving a heating device 10. The heating device 10, when activated, heats the liquid inside the sump 15.

In different embodiments, nevertheless, the bottom region of the washing tub may be configured differently. For example, the bottom region of the washing tub may not comprise a seat for the heating device. The heating device may be advantageously placed in the annular gap between the washing tub and the washing drum.

Preferably, the laundry washing machine 1 comprises a device 19 suited to detect the liquid level inside the washing tub 3.

The sensor device 19 preferably comprises a pressure sensor which senses the pressure in the washing tub 3. From the values sensed by the sensor device 19 it is possible to determine the liquid level of the liquid inside the washing tub 3. In another embodiment, not illustrated, laundry washing machine may preferably comprise (in addition to or as a replacement of the pressure sensor) a level sensor (for example mechanical, electro-mechanical, optical, etc.) adapted to detect the liquid level inside the washing tub 3.

A water supply circuit 5 is preferably arranged in the upper part of the laundry washing machine 1 and is suited to supply water into the washing tub 3 from an external water supply line E. The water supply circuit 5 preferably comprises a controlled supply valve 5 a which is properly controlled, opened and closed, during the washing cycle. The water supply circuit of a laundry washing machine is well known in the art, and therefore it will not be described in detail.

The laundry washing machine 1 advantageously comprises a treating agents dispenser 14 to supply one or more treating agents into the washing tub 3 during a washing cycle. Treating agents may comprise, for example, detergents, rinse additives, fabric softeners or fabric conditioners, waterproofing agents, fabric enhancers, rinse sanitization additives, chlorine-based additives, etc.

Preferably, the treating agents dispenser 14 comprises a removable drawer 6 provided with various compartments suited to be filled with treating agents.

In a preferred embodiment, not illustrated, the treating agents dispenser may comprise a pump suitable to convey one or more of said agents from the dispenser to the washing tub.

In the preferred embodiment here illustrated, the water is supplied into the washing tub 3 from the water supply circuit 5 by making it flow through the treating agents dispenser 14 and then through a supply pipe 18.

In an alternative embodiment of the invention, a further separate water supply pipe can be provided, which supplies exclusively clean water into the washing tub from the external water supply line.

In further preferred embodiments, not illustrated herein, a water softening device may preferably be arranged/interposed between the external water supply line and the treating agents dispenser so as to be crossed by the fresh water flowing from the external water supply line. The water softening device, as known, is structured for reducing the hardness degree of the fresh water drawn from the external water supply line and conveyed to the treating agents dispenser.

In a different embodiment, the water softening device may be arranged/interposed between the external water supply line and the washing tub, so as to be crossed by the fresh water flowing from the external water supply line and conveying it directly to the washing tub.

Laundry washing machine 1 preferably comprises a water outlet circuit 25 suitable for withdrawing liquid from the bottom region 3 a of the washing tub 3.

The water outlet circuit 25 preferably comprises a main pipe 17, a draining pump 27 and an outlet pipe 28 ending outside the cabinet 2.

The water outlet circuit 25 preferably further comprises a filtering device 12 arranged between the main pipe 17 and the draining pump 27. The filtering device 12 is adapted to retain all the undesirable bodies (for example buttons that have come off the laundry, coins erroneously introduced into the laundry washing machine, etc.). The filtering device 12 can preferably be removed, and then cleaned, through a gate 13 placed advantageously on the front wall of the cabinet 2 of the laundry washing machine 1, as illustrated in FIG. 1.

The main pipe 17 connects the bottom region 3 a of the washing tub 3 to the filtering device 12.

In a further embodiment, not illustrated, the filtering device 12 may be provided directly in the washing tub 3, preferably obtained in a single piece construction with the latter. In this case, the filtering device 12 is fluidly connected to the outlet of the washing tub 3, in such a way that water and washing liquid drained from the washing tub 3 enters the filtering device 12.

Activation of the draining pump 27 drains the liquid, i.e. dirty water or water mixed with washing and/or rinsing products, from the washing tub 3 to the outside.

According to the invention, the laundry washing machine 1 preferably comprises a recirculation system 20 which is adapted to drain liquid from the bottom region 3 a of the washing tub 3 and to re-admit such a liquid into a first region 3 b of the washing tub 3, as better described below.

Preferably, the first region 3 b of the washing tub 3 substantially corresponds to an upper region 3 b of the washing tub 3. The liquid is preferably re-admitted to the upper region 3 b of the washing tub 3 in order to improve wetting of the laundry inside the washing drum 4. This action is preferably carried out at the beginning of a washing cycle when the laundry needs to be completely soaked. Furthermore, this action is preferably carried out during rinsing phases at the beginning of the washing cycle or during rinsing phases in successive steps of the washing cycle.

The recirculation system 20 preferably comprises a first recirculation circuit 30 for conveying liquid to the first region 3 b of the washing tub 3.

The first recirculation circuit 30 preferably comprises a first duct 33 terminating at said first region 3 b, preferably ending at the bellows. The first duct 33 is preferably provided with a terminal nozzle 33 a.

The recirculation system 20 preferably comprises a recirculation pump 22 having an outlet 26 connected to the first recirculation circuit 30 for conveying liquid to the first recirculation circuit 30, more preferably to the first duct 33.

The recirculation pump 22 preferably comprises a pump chamber, not shown, having an inlet 24 connected to the bottom 3 a of the washing tub 3. Inlet 24 of the recirculation pump 22 is preferably connected to the bottom 3 a of the washing tub 3 through a suction pipe 32 preferably connected to the filtering device 12.

The pump chamber of the recirculation pump 22 then communicates with the outlet 26 for conveying liquid, as said above, to the first recirculation circuit 30, more preferably to the first duct 33.

According to an advantageous aspect of the invention, the recirculation pump 22 comprises a variable speed pump. The variable speed recirculation pump 22 is therefore operable at variable speeds to circulate liquid through the first recirculation circuit 30, more preferably through the first duct 33.

In the following, we will refer to the control of the recirculation pump 22 during a recirculation phase of a washing cycle carried out in the laundry washing machine 1 of the invention.

The control of the recirculation pump 22 according to the present invention is preferably carried out during the recirculation phase in main washing phase. The main washing phase, as known, preferably comprises mechanical and/or chemical treating of the laundry by rotating the washing drum and by adding detergent and water inside the washing tub 3. During the main washing phase the laundry needs to be completely soaked and the recirculation phase is advantageously carried out.

Anyway, control of the recirculation pump 22 according to the present invention may be carried out during the recirculation phase in other phases of a washing cycle, for example in any rinsing phase which follows the main washing phase.

After the main washing phase, laundry needs to be cleaned and steps of adding clean water, rotating the washing drum and draining water extracted from the laundry are preferably carried out. Said steps may be consecutively carried out two or more times.

Addition of clean water is advantageously carried through a recirculation phase according to the invention.

According to an advantageous aspect of the invention, the rotation speed Rs of the recirculation pump 22 is varied depending to the difference between the detected liquid level Ld inside the washing tub 3 and a prefixed liquid level value Lp.

The detected liquid level Ld is preferably obtained by means of the sensor device 19.

According to a preferred embodiment of the invention, the prefixed liquid level value Lp is preferably set as a value at which liquid inside the washing tub 3 is above the heating device 10. Preferably, the prefixed liquid level value Lp is also set as a value at which liquid inside the washing tub 3 is below the lower point of the washing drum 4.

In further preferred embodiments, the prefixed liquid level value Lp is set above the lower point of the washing drum 4 and part of the liquid wet the laundry inside the washing drum 4 thereby improving wetting of the laundry.

Variation of the rotation speed Rs of the recirculation pump 22 according to the invention, as better explained below, is carried out while the recirculation pump 22 is active.

According to an advantageous aspect of the invention, the recirculation pump 22 is preferably activated when the detected liquid level Ld is above the prefixed liquid level value Lp. On the contrary, the recirculation pump 22 is preferably deactivated when the detected liquid level Ld is equal to, or goes below to, the prefixed liquid level value Lp.

For example, referring to a rinsing phase which follows the main washing phase, an amount of clean water is introduced into the washing tub 3, preferably through the water supply system 5, and once the water goes above the prefixed liquid level value Lp the recirculation pump 22 is activated.

Preferably, according to the invention, the rotation speed Rs of the recirculation pump 22 is varied so that the rotation speed Rs is directly proportional to the difference between the detected liquid level Ld and the prefixed liquid level value Lp. The rotation speed Rs is therefore preferably evaluated as a function of the detected liquid level Ld as follows:

Rs=k*(Ld−Lp) if Ld>Lp

Rs=0 if Ld≤Lp

wherein k is the coefficient of proportionality.

When the detected liquid level Ld increases above the prefixed liquid level value Lp, the rotation speed Rs of the recirculation pump 22 is also increased, preferably according to said function, so that the liquid flowing through the first recirculation circuit 30, more preferably through the first duct 33, is in turn increased. Soaking speed of the laundry is therefore increased.

At the same time, the level of the liquid inside the washing tub 3 is controlled in order to be maintained as much as possible close to, and preferably above, the prefixed liquid level value Lp.

The aim of the control of the recirculation pump 22 according to the invention is to circulate the maximum quantity of liquid through the first recirculation circuit 30, more preferably through the first duct 33, while assuring that the liquid level inside the washing tub 3 is above the prefixed liquid level value Lp.

Advantageously, either a good soaking of the laundry is reached and a minimum amount of liquid inside the washing tub 3 is assured thus avoiding suction cavitation for the recirculation pump 22.

According to a preferred embodiment of the invention, the recirculation pump 22 is controlled so that its rotation speed Rs does not go above a maximum threshold value Rsmax.

In such a case, even if the difference between the detected liquid level Ld and the prefixed liquid level value Lp has a high value, the rotation speed Rs is limited to said maximum threshold value Rsmax.

A maximum threshold value Rsmax is preferably chosen in order to limit the noise and/or vibrations generated by the recirculation pump 22.

According to a preferred embodiment of the invention, the recirculation pump 22 is controlled so that its minimum rotation speed Rs is equal to a minimum threshold value Rsmin greater than 0.

Preferably in such a case the rotation speed Rs is preferably evaluated as a function of the detected liquid level Ld as follows:

Rs=k*(Ld−Lp)+Rsmin if Ld>Lp

Rs=0 if Ld≤Lp

In a preferred embodiment, the rotation speed Rs of the recirculation pump 22 is varied over the time according to a continuous function.

In a further preferred embodiment, the rotation speed Rs of the recirculation pump 22 is varied over the time according to a step function.

According to an advantageous aspect of the invention, the method further comprises a step of controlling when the liquid level goes below the prefixed liquid level value Lp and taking one or more actions accordingly.

Preferably, as already mentioned above, when the liquid level is equal to, or goes below to, the prefixed liquid level value Lp the recirculation pump 22 is deactivated.

In a preferred embodiment of the invention, the method comprises a step of reestablishing the prefixed liquid level value Lp inside the washing tub 3 when the liquid level goes below the prefixed liquid level value Lp.

In a first preferred embodiment of the invention, the step of reestablishing the prefixed liquid level value Lp inside the washing tub 3 is carried out by conveying an amount of water into the washing tub 3. Preferably said amount of water is supplied into the washing tub through the water supply system 5. The water introduced into the washing tub 3 has the scope of bringing the liquid level inside the washing tub 3 above the prefixed liquid level value Lp so that the recirculation pump 22 may be activated again and its rotation speed Rs controlled according to the above-described methodology.

In another preferred embodiment of the invention, the step of reestablishing the prefixed liquid level value Lp is carried out by extracting an amount of water from the laundry in a dewatering process.

The dewatering process is preferably carried out by rotating the washing drum 4 at a dewatering speed Ds wherein, preferably, at the dewatering speed Ds the laundry stuck to the inner side wall of the washing drum 4 and water is expelled under the action of centrifugal force.

FIGS. 3 to 8 show a further preferred embodiment of the invention which differs from the preferred embodiment previously described in that the recirculation system 120 comprises a further recirculation circuit. In the drawings, corresponding characteristics and/or components of the first embodiment previously described are identified by the same reference numbers.

The recirculation system 120 is adapted to drain liquid from the bottom region 3 a of the washing tub 3 and to re-admit such a liquid into a first region 3 b and a second region 3 a of the washing tub 3, as better described below.

Preferably, the first region 3 b of the washing tub 3 substantially corresponds to the upper region 3 b of the washing tub 3, as described above with reference to the first embodiment illustrated in FIGS. 1 and 2. The liquid is preferably re-admitted to the upper region 3 b of the washing tub 3 in order to improve wetting of the laundry inside the washing drum 4. This action, as said above, is preferably carried out at the beginning of a washing cycle, during washing or rinsing phases at the beginning of the washing cycle or during rinsing phases in successive steps of the washing cycle.

Preferably, the second region 3 a of the washing tub 3 substantially corresponds to the same bottom region 3 a of the washing tub 3. The liquid is preferably re-admitted to the bottom region 3 a of the washing tub 3 for the mixing and/or the dissolution of the products, in particular of the detergent. Mixing and/or dissolution of a product is preferably carried out during a washing cycle when one of the products is supplied into the washing tub 3 from the treating agents dispenser 14.

The recirculation system 120 preferably comprises a first recirculation circuit 30 for conveying liquid to the first region 3 b of the washing tub 3 and a second recirculation circuit 40 for conveying liquid to the second region 3 a of the washing tub 3.

The first recirculation circuit 30 preferably comprises a first duct 33 terminating at said first region 3 b, preferably ending at the bellows 7, as better illustrated in FIG. 4. The first duct 33 is preferably provided with a terminal nozzle 33 a.

The second recirculation circuit 40 preferably comprises a second duct 43 terminating at said second region 3 a, preferably ending inside the sump 15. The second duct 43 is preferably provided with a terminal nozzle 43 a.

The recirculation system 120 then preferably comprises a common variable speed recirculation pump 122 for conveying liquid to the first and second recirculation circuits 30, 40, more preferably to the first and second ducts 33, 43.

The recirculation pump 122 preferably comprises a pump chamber 123 having an inlet 124 connected to the bottom 3 a of the washing tub 3. Inlet 124 of the recirculation pump 122 is preferably connected to the bottom 3 a of the washing tub 3 through a suction pipe 32 preferably connected to the filtering device 12.

The recirculation pump 122 then preferably has an outlet arrangement 126 for conveying liquid from the pump chamber 123 to the first and second recirculation circuits 30, 40.

The pump chamber 123 preferably receives an impeller 123 a apt to be rotated and to force liquid from the pump chamber 123 towards the outlet arrangement 126, as illustrated in FIG. 8

The pump chamber 123 preferably has a substantially cylindrical shape.

In a preferred embodiment of the invention and according to FIGS. 5 to 8, the outlet arrangement 126 preferably comprises a first outlet 158 a connected to the first duct 33 and a second outlet 158 b connected to the second duct 43.

The first outlet 158 a preferably comprises a portion of duct which extends tangentially from the pump chamber 123.

The second outlet 158 b preferably comprises a portion of duct which extends tangentially from the pump chamber 123.

First and the second outlets (ducts) 158 a, 158 b are preferably parallel one to the other.

Preferably, first and second outlets 158 a, 158 b are preferably realized at a body portion 150 of the recirculation pump 122.

Preferably, the recirculation circuits 30, 40 are configured so that the liquid in the second recirculation circuit 40 requires a pressure P2 to reach the second region 3 a of washing tub 3 which is lower than the pressure P1 required for the liquid in the first recirculation circuit 30 to reach the first region 3 b of the washing tub 3. More preferably, the ducts 33, 43 are configured so that the liquid in the second duct 43 requires a pressure P2 to reach the second region 3 a of the washing tub 3 which is lower than the pressure P1 required for a liquid in the first duct 33 to reach the first region 3 b of the washing tub 3.

It should be noted that the pressure required for the liquid in the second duct 43 to reach the second region 3 a of the washing tub 3 may vary according to the operational condition of the same second recirculation circuit 40.

Namely, the pressure required for the liquid in the second duct 43 to reach the second region 3 a of the washing tub 3 while the liquid level inside the washing tub 3 is lower than the position of the terminal nozzle 43 a, has a first value P2 which is lower than the value P2′ of the pressure required for the liquid in the second duct 43 to reach the second region 3 a of the washing tub 3 while the liquid level inside the washing tub 3 is equal or higher than the position of the terminal nozzle 43 a.

At the same time, the value P1 of the pressure required for the liquid in the first duct 33 to reach the first region 3 b of the washing tub 3 does not vary according to the operational conditions of the second recirculation circuit 40.

Said pressure value P1 has the same value irrespective of the liquid level inside the washing tub 3.

In any case, said pressure values P2, P2′ required for the liquid in the second duct 43 to reach the second region 3 a of the washing tub 3 are lower than the pressure value P1 required for the liquid in the first duct 33 to reach the first region 3 b of the washing tub 3

According to the preferred embodiment illustrated herein, the first duct 33 preferably defines a first volume V1. The first volume V1 is closely related to the size of the first duct 33 and preferably depends on diameter and length of the same. Analogously, the second duct 43 preferably defines a second volume V2. The second volume V2 is closely related to the size of the second duct 43 and preferably depends on diameter and length of the same.

According to the spatial arrangement of the components of the recirculation system 120, in particular the position of the recirculation pump 122 and the layout of the ducts 33, 43, the second volume V2 defined by the second duct 43 is lower than the first volume V1 defined by the first duct 33.

The second duct 43 preferably comprises a second pipe connecting the second outlet 158 b to the lower region 3 a of the washing tub 3. The first duct 33 preferably comprises a first pipe, substantially having the same diameter of the second pipe but much longer than the second pipe, connecting the first outlet 158 a to the upper region 3 b of the washing tub 3.

Preferably, in such a case, the recirculation circuits 30, 40 are configured so that the liquid in the second recirculation circuit 40 requires a pressure P2 to fill the second volume V2 and then to reach the second region 3 a of washing tub 3 which is lower than the pressure P1 required for the liquid to fill the first volume V1 in the first recirculation circuit 30 and to reach the first region 3 b of the washing tub 3.

More preferably, in such a case, the ducts 33, 43 are configured so that the liquid in the second duct 43 requires a pressure P2 to fill the second volume V2 and then to reach the second region 3 a of washing tub 3 which is lower than the pressure P1 required for the liquid to fill the first volume V1 in the first duct 33 and to reach the first region 3 b of the washing tub 3.

In different embodiments, ducts of the recirculation system may be differently configured to achieve the same effect.

For example, the first and the second duct may have the same volume but extending at different heights.

According to an advantageous aspect of the invention, the recirculation pump 122 comprises a bi-directional variable speed pump operable in a first direction of rotation R1 and in a second direction of rotation R2 opposite to the first direction R1.

It has to be noted that saying that the recirculation pump 122 is operable in a first direction of rotation R1 means that the impeller 123 a is rotatable in the first direction of rotation R1 and saying that the recirculation pump 122 is operable in a second direction of rotation R2 opposite to the first direction R1 means that the impeller 123 a is rotatable in the second direction of rotation R2 opposite to the first direction R1.

According to an advantageous aspect of the invention, therefore, the impeller 123 a may be rotated in the first direction of rotation R1 and in the second direction of rotation R2 opposite to the first direction R1.

The two directions R1 and R2 are depicted in particular in FIGS. 5 and 8.

According to an advantageous aspect of the invention, the recirculation pump 122 is operated in the first direction R1 to circulate liquid in the first duct 33 through the first outlet 158 a to reach the washing tub 3 and is operated in the second direction R2 to circulate liquid in the second duct 43 through the second outlet 158 b to reach the washing tub 3.

In other words, preferably, the impeller 123 a is rotated in the first direction R1 to circulate liquid in the first duct 33 through the first outlet 158 a to reach the washing tub 3 and is rotated in the second direction R2 to circulate liquid in the second duct 43 through the second outlet 158 b to reach the washing tub 3.

As illustrated in FIG. 8, the pump chamber 123, the impeller 123 a, first and second outlets 158 a, 158 b are shaped so that when the impeller 123 a rotates in the first direction R1 the liquid forced by the impeller 123 a itself principally meets the first outlet 158 a and, vice versa, when the impeller 123 a rotates in the second direction R2 the liquid forced by the impeller 123 a itself principally meets the second outlet 158 b.

Preferably, the recirculation pump 122 is operated in the first direction R1 to circulate liquid in the first duct 33 and to spray liquid inside the washing tub 3 through the terminal nozzle 33 a, more preferably sprayed over the laundry inside the washing drum 4.

More preferably, the variable speed recirculation pump 122 is operable at variable speeds in the first direction R1 to circulate liquid through the first recirculation circuit 30, more preferably through the first duct 33, during a recirculation phase of a washing cycle carried out in the laundry washing machine of the invention.

Control of the rotation speed Rs of the recirculation pump 122 in the first direction R1 of rotation is carried out according to the invention as described above with reference to the control of the recirculation pump 22 of the first preferred embodiment shown in FIGS. 1 and 2. Therefore, the rotation speed Rs of the recirculation pump 122 in the first direction of rotation R1 is varied depending to the difference between the detected liquid level Ld inside the washing tub 3 and a prefixed liquid level value Lp, as shown in FIG. 3. What has been described for the first preferred embodiment shown in FIGS. 1 and 2 with reference to the control of the recirculation pump 22 shall therefore apply mutatis mutandis to the control of the recirculation pump 122 while rotating in the first direction R1 of rotation.

Advantageously, all the effects and/or advantages above-mentioned with reference to the first embodiment relating the control of the recirculation pump are achieved.

Preferably, then, the recirculation pump 122 is operated in the second direction R2 to circulate liquid only in the second duct 43 through the second outlet 158 b to reach the washing tub 3.

When the recirculation pump 122 is operated in the second direction R2, the liquid circulates in the second duct 43 and is sprayed inside the washing tub 3 through the terminal nozzle 43 a, more preferably sprayed inside the sump 15.

Advantageously, during the washing cycle when the liquid needs to be re-admitted to the bottom region 3 a of the washing tub 3, for example for the mixing and/or the dissolution of the products, the recirculation pump 122 is operated in the second direction R2.

Preferably, the recirculation pump 122 may be operated in the second direction R2 either at a predetermined fixed speed S2 or at a speed s2 varying over time.

In the latest, the liquid is preferably re-admitted to the bottom region 3 a of the washing tub 3 at a variable speed. Said variation of speed causes a respective variation of the flow rate of the liquid circulating in the second duct 43. In turn, the liquid is sprayed inside the sump 15 through the terminal nozzle 43 a at variable intensity. This advantageously enhances mixing and/or dissolution of the products.

In a preferred embodiment, the second speed s2 of the recirculation pump 122 in the second direction R2 varies according to a step function.

In a further preferred embodiment, the second speed s2 of the recirculation pump 122 in the second direction R2 varies according to a continuous function.

FIGS. 9 to 13 show a further preferred embodiment of the invention which differs from the preferred embodiment previously described with reference to FIGS. 3 to 8 in the shape of the recirculation pump 222. In the drawings, corresponding characteristics and/or components of the embodiments previously described are identified by the same reference numbers.

The recirculation system 220 preferably comprises a common bi-directional variable speed recirculation pump 222 for conveying liquid to the first and second recirculation circuits 30, 40, more preferably to the first and second ducts 33, 43.

The recirculation pump 222 preferably comprises a pump chamber 223 having an inlet 224 connected to the bottom 3 a of the washing tub 3. Inlet 224 of the recirculation pump 222 is preferably connected to the bottom 3 a of the washing tub 3 through a suction pipe 32 preferably connected to the filtering device 12.

The recirculation pump 222 then preferably has an outlet arrangement 226 for conveying liquid from the pump chamber 223 to the first and second recirculation circuits 30, 40.

The pump chamber 223 preferably receives an impeller 223 a apt to be rotated and to force liquid from the pump chamber 223 towards the outlet arrangement 226.

The pump chamber 223 preferably has a substantially cylindrical shape.

The outlet arrangement 226 preferably comprises a first outlet 258 a connected to the first duct 33 and a second outlet 258 b connected to the second duct 43.

The first outlet 258 a preferably comprises a portion of duct which extends obliquely from the pump chamber 223.

The second outlet 258 b preferably comprises a portion of duct which extends obliquely from the pump chamber 223.

First and the second outlets (ducts) 258 a, 258 b are preferably parallel one to the other.

Preferably, first and second outlets 258 a, 258 b are preferably realized at a body portion 250 of the recirculation pump 222.

According to the advantageous aspect of the invention, the recirculation pump 222 is operated in a first direction R1 to circulate liquid in the first duct 33 through the first outlet 258 a to reach the washing tub 3 and is operated in a second direction R2 to circulate liquid in the second duct 43 through the second outlet 258 b to reach the washing tub 3.

In other words, preferably, the impeller 223 a is rotated in the first direction R1 to circulate liquid in the first duct 33 through the first outlet 258 a to reach the washing tub 3 and is rotated in the second direction R2 to circulate liquid in the second duct 43 through the second outlet 258 b to reach the washing tub 3.

As illustrated in FIG. 13, the pump chamber 223, the impeller 223 a, first and second outlets 258 a, 258 b are shaped so that when the impeller 223 a rotates in the first direction R1 the liquid forced by the impeller 223 a itself principally meets the first outlet 258 a and, vice versa, when the impeller 223 a rotates in the second direction R2 the liquid forced by the impeller 223 a itself principally meets the second outlet 258 b.

Advantageously, control of the rotation speed Rs of the recirculation pump 222 in the first direction R1 of rotation is carried out according to the invention as described above with reference to the control of the recirculation pump 22 of the first preferred embodiment shown in FIGS. 1 and 2. Therefore, the rotation speed Rs of the recirculation pump 222 in the first direction of rotation R1 is varied depending to the difference between the detected liquid level Ld and a prefixed liquid level value Lp. What has been described for the first preferred embodiment shown in FIGS. 1 and 2 with reference to the control of the recirculation pump 22 shall therefore apply mutatis mutandis to the control of the recirculation pump 222 while rotating in the first direction R1 of rotation.

Advantageously, all the effects and/or advantages above-mentioned with reference to the first embodiment relating the control of the recirculation pump are achieved.

FIGS. 14 to 18 show a further preferred embodiment of the invention which differs from the preferred embodiments previously described in the shape of the recirculation pump 322. In the drawings, corresponding characteristics and/or components of the embodiments previously described are identified by the same reference numbers.

The recirculation system 320 preferably comprises a common bi-directional variable speed recirculation pump 322 for conveying liquid to the first and second recirculation circuits 30, 40, more preferably to the first and second ducts 33, 43.

The recirculation pump 322 preferably comprises a pump chamber 323 having an inlet 324 connected to the bottom 3 a of the washing tub 3. Inlet 324 of the recirculation pump 322 is preferably connected to the bottom 3 a of the washing tub 3 through a suction pipe 32 preferably connected to the filtering device 12.

The recirculation pump 322 then preferably has an outlet arrangement 326 for conveying liquid from the pump chamber 323 to the first and second recirculation circuits 30, 40.

The pump chamber 323 preferably receives an impeller 323 a apt to be rotated and to force liquid from the pump chamber 323 towards the outlet arrangement 326.

The pump chamber 323 preferably has a substantially cylindrical shape.

The outlet arrangement 326 preferably comprises a common outlet portion 358 from the pump chamber 323 and a bifurcation 360 having a first outlet 360 a for the first duct 33 and a second outlet 360 b for the second duct 43.

Preferably, common outlet portion 358 and bifurcation 360 are realized at a body portion 350 of the pump recirculation 322.

The bifurcation 360 is preferably substantially Y shaped and configured so that the two ducts 33, 43 preferably extend upwardly from the bifurcation 360.

According to the advantageous aspect of the invention, the recirculation pump 322 is operated in a first direction R1 to circulate liquid in the first duct 33 to reach the washing tub 3 and is operated in a second direction R2 to circulate liquid in the second duct 43 to reach the washing tub 3.

In other words, preferably, the impeller 323 a is rotated in the first direction R1 to circulate liquid in the first duct 33 to reach the washing tub 3 and is rotated in the second direction R2 to circulate liquid in the second duct 43 to reach the washing tub 3.

Advantageously, control of the rotation speed Rs of the recirculation pump 322 in the first direction R1 of rotation is carried out according to the invention as described above with reference to the control of the recirculation pump 22 of the first preferred embodiment shown in FIGS. 1 and 2. Therefore, the rotation speed Rs of the recirculation pump 322 in the first direction of rotation R1 is varied depending to the difference between the detected liquid level Ld inside a washing tub 3 and a prefixed liquid level value Lp. What has been described for the first preferred embodiment shown in FIGS. 1 and 2 with reference to the control of the recirculation pump 22 shall therefore apply mutatis mutandis to the control of the recirculation pump 322 while rotating in the first direction R1 of rotation.

Advantageously, all the effects and/or advantages above-mentioned with reference to the first embodiment relating the control of the recirculation pump are achieved.

FIGS. 19 to 23 show a further preferred embodiment of the invention. In the drawings, corresponding characteristics and/or components of the embodiments previously described are identified by the same reference numbers.

The recirculation system 420 preferably comprises a common variable speed recirculation pump 422 comprising an inlet 424 connected to the bottom 3 a of the washing tub 3 and an outlet 426 for conveying liquid to the first and second recirculation circuits 30, 40, more preferably to the first and second ducts 33, 43.

Inlet 424 of the recirculation pump 422 is preferably connected to the bottom 3 a of the washing tub 3 through a pipe 32 preferably connected to the filtering device 12.

According to an aspect of the invention, outlet 426 of the recirculation pump 422 conveys liquid to the first duct 33 and the second duct 43 through a bifurcation 460.

Preferably, an outlet duct 462 is connected to the pump outlet 426 and the bifurcation 460 is realized at an outlet duct end 462 a thereof. The bifurcation 460 is preferably Y shaped.

Preferably, the liquid continuously flows from the inlet duct 424 concurrently to the first duct 33 and the second duct 43.

According to an advantageous aspect of the invention, the recirculation pump 422 is operated at a first speed s1 to circulate liquid only in the second recirculation circuit 40 to reach the washing tub 3 and the recirculation pump 422 is operated at a second speed s2 to circulate liquid both in the first recirculation circuit 30 and the second recirculation circuit 40 to reach the washing tub 3.

More preferably, the recirculation pump 422 is operated at a first speed s1 to circulate liquid only in the second duct 43 to reach the washing tub 3 and the recirculation pump 422 is operated at a second speed s2 to circulate liquid both in the first duct 33 and the second duct 43 to reach the washing tub 3.

It should be noted that when the recirculation pump 422 is operated at the first speed s1, the liquid may partially fill the first recirculation circuit 30, in particular the first duct 33, but it does not reach the washing tub 3.

Advantageously, during the washing cycle when the liquid needs to be re-admitted to the bottom region 3 a of the washing tub 3, for example for the mixing and/or the dissolution of the products, the recirculation pump 422 is operated at a first speed s1. When the liquid needs to be re-admitted to the upper region 3 b of the washing tub 3, preferably to soak the laundry, the recirculation pump 422 is operated at a second speed s2 higher than the first speed s1. In the latest, liquid is also re-admitted to the bottom region 3 a of the washing tub 3 through the second recirculation circuit 40.

Nevertheless, re-admission of the liquid to the bottom region 3 a of the washing tub 3 is accepted since it does not negatively affect the soaking process.

According to an aspect of the invention, with the recirculation pump 422 operated at the first speed s1 the liquid may circulate only in the second recirculation circuit 40 and not in the first recirculation circuit 30 thanks to the asymmetry of the two lines 30, 40.

Preferably, at this purpose, the recirculation circuits 30, 40 are configured so that the liquid in the second recirculation circuit 40 requires a pressure P2 to reach the second region 3 a of washing tub 3 which is lower than the pressure P1 required for the liquid in the first recirculation circuit 30 to reach the first region 3 b of the washing tub 3. Symmetry of the two lines 30, 40 must therefore be avoided. More preferably, the ducts 33, 43 are configured so that the liquid in the second duct 43 requires a pressure P2 to reach the second region 3 a of the washing tub 3 which is lower than the pressure P1 required for a liquid in the first duct 33 to reach the first region 3 a of the washing tub 3. Symmetry of the two ducts 33, 43 must therefore be avoided.

It should be noted that the pressure required for the liquid in the second duct 43 to reach the second region 3 a of the washing tub 3 may vary according to the operational condition of the same second recirculation circuit 40.

Namely, the pressure required for the liquid in the second duct 43 to reach the second region 3 a of the washing tub 3 while the liquid level inside the washing tub 3 is lower than the position of the terminal nozzle 43 a, has a first value P2 which is lower than the value P2′ of the pressure required for the liquid in the second duct 43 to reach the second region 3 a of the washing tub 3 while the liquid level inside the washing tub 3 is equal or higher than the position of the terminal nozzle 43 a.

At the same time, the value P1 of the pressure required for the liquid in the first duct 33 to reach the first region 3 b of the washing tub 3 does not vary according to the operational condition of the second recirculation circuit 40.

Said pressure value P1 has the same value irrespective of the liquid level inside the washing tub 3.

In any case, and according to the invention, said pressure values P2, P2′ for the liquid in the second duct 43 to reach the second region 3 a of washing tub 3 are lower than the pressure value P1 for the liquid in the first duct 33 to reach the first region 3 b of the washing tub 3.

According to the preferred embodiment illustrated herein, the second duct 43 preferably defines a second volume V2. The second volume V2 is closely related to the size of the second duct 43 and preferably depends on diameter and length of the same. Analogously, the first duct 33 preferably defines a first volume V1. The first volume V1 is closely related to the size of the first duct 33 and preferably depends on diameter and length of the same.

According to the spatial arrangement of the components of the recirculation system 420, in particular the position of the recirculation pump 422 and the layout of the ducts 33, 43, the second volume V2 defined by the second duct 43 is lower than the first volume V1 defined by the first duct 33.

The second duct 43 preferably comprises a second pipe connecting the bifurcation 460 to the lower region 3 a of the washing tub 3. The first duct 33 preferably comprises a first pipe, substantially having the same diameter of the second pipe but much longer than the second pipe, connecting the bifurcation 460 to the upper region 3 b of the washing tub 3.

Preferably, in such a case, the recirculation circuits 30, 40 are configured so that the liquid in the second recirculation circuit 40 requires a pressure P2 to fill the second volume V2 and then to reach the second region 3 a of the washing tub 3 which is lower than the pressure P1 required for the liquid to fill the first volume V1 in the first recirculation circuit 30 and to reach the first region 3 b of the washing tub 3.

More preferably, in such a case, the ducts 33, 43 are configured so that the liquid in the second duct 43 requires a pressure P2 to fill the second volume V2 and then to reach the second region 3 a of washing tub 3 which is lower than the pressure P1 required for the liquid to fill the first volume V1 in the first duct 33 and to reach the first region 3 b of the washing tub 3.

In different embodiments, ducts of the recirculation system may be differently configured to achieve the same effect.

For example, the first and the second duct may have the same volume but extending at different highs.

When the recirculation pump 422 is operated at the first speed s1, a proper pressure is maintained at its outlet 426 so that the liquid in the second duct 43 reaches the second region 3 a of washing tub 3 while the liquid in the first duct 33 does not reach the first region 3 b of the washing tub 3.

When the recirculation pump 422 is operated at the second speed s2, a proper pressure is maintained at its outlet 26 so that the liquid in the second duct 43 reaches the second region 3 a of washing tub 3 and the liquid in the first duct 33 reaches the first region 3 b of the washing tub 3.

According to an aspect of the invention, and according to the above description, it can be appreciated that the recirculation system 420 shows a threshold point between a condition wherein the liquid circulates only in the second recirculation circuit 40, or second duct 43, and a condition wherein the liquid circulates both in the first recirculation circuit 30 and the second recirculation circuit 40, or ducts 33, 43. Correspondingly, the recirculation pump 422 shows a speed threshold RSt wherein if the recirculation pump 422 is operated at a speed below, or equal to, the speed threshold RSt the liquid circulates only in the second recirculation circuit 40, or second duct 43, and if the recirculation pump 422 is operated at a speed above the speed threshold RSt the liquid circulates both in the first recirculation circuit 30 and the second recirculation circuit 40, or ducts 33, 43.

Preferably, the recirculation pump 422 is operated at a second speed s2 above the speed threshold RSt to circulate liquid in the first duct 33 and to spray liquid inside the washing tub 3 through the terminal nozzle 33 a, more preferably sprayed over the laundry inside the washing drum 4.

More preferably, the variable speed recirculation pump 422 is operable at variable speeds above the speed threshold RSt to circulate liquid through the first recirculation circuit 30, more preferably to the first duct 33, during a recirculation phase of a washing cycle carried out in the laundry washing machine of the invention.

Control of the rotation speed Rs of the recirculation pump 422 is carried out according to the invention as described above with reference to the control of the recirculation pump 22 of the first preferred embodiment shown in FIGS. 1 and 2. In particular, the rotation speed Rs of the recirculation pump 422 is varied depending to the difference between the detected liquid level Ld inside the washing tub 3 and a prefixed liquid level value Lp. A minimum threshold rotation speed Rsmin is preferably set for the recirculation pump 420.

The minimum threshold value Rsmin is preferably set equal to, or greater than, said speed threshold RSt.

Preferably, in such a case, the rotation speed Rs is evaluated as a function of the detected liquid level Ld as follows:

Rs=k*(Ld−Lp)+Rsmin if Ld>Lp

Rs=0 if Ld≤Lp

with the condition that Rsmin≥RSt.

Advantageously, all the effects and/or advantages above-mentioned with reference to the first embodiment relating the control of the recirculation pump are achieved.

It has thus been shown that the present invention allows all the set objects to be achieved.

In particular, it makes it possible to provide a method for controlling a recirculation pump in a laundry washing machine which improves wetting of laundry during a recirculation phase compared to known techniques.

While the present invention has been described with reference to the particular embodiments shown in the figures, it should be noted that the present invention is not limited to the specific embodiments illustrated and described herein; on the contrary, further variants of the embodiments described herein fall within the scope of the present invention, which is defined in the claims. 

1. A method for operating a laundry washing machine comprising: a washing drum configured to receive laundry to be washed; a washing tub external to the washing drum; a water supply system configured to convey water to the washing tub; a recirculation system comprising a recirculation circuit configured to drain liquid from a bottom of the washing tub and to re-admit the liquid into a first region of the washing tub, the recirculation system comprising a variable speed recirculation pump having an outlet connected to the recirculation circuit and wherein the recirculation pump is operable at variable rotation speeds to circulate liquid through the recirculation circuit; a liquid level sensor device configured to detect a liquid level inside the washing tub; wherein the method comprises operating the recirculation system in a recirculation phase to drain the liquid from the bottom of the washing tub and to re-admit the liquid into the first region of the washing tub through the recirculation circuit, wherein the recirculation phase comprises: determining a detected liquid level using the liquid level sensor device; determining a difference between the detected liquid level and a prefixed liquid level value; and the step of controlling the recirculation pump by varying a rotation speed of the recirculation pump depending to the difference between the detected liquid level and the prefixed liquid level value.
 2. The method according to claim 1, wherein the recirculation phase further comprises activating the recirculation pump when the detected liquid level is above the prefixed liquid level value.
 3. The method according to claim 1, wherein the recirculation phase further comprises deactivating the recirculation pump when the detected liquid level is equal to, or below the prefixed liquid level value.
 4. The method according to claim 1, wherein controlling the recirculation pump by varying the rotation speed of the recirculation pump comprises operating the rotation speed of the recirculation pump to be directly proportional to the difference between the detected liquid level and the prefixed liquid level value.
 5. The method according to claim 1, wherein controlling the recirculation pump by varying the rotation speed of the recirculation pump comprises maintaining the rotation speed of the recirculation pump between a minimum threshold value and a maximum threshold value.
 6. The method according to claim 5, wherein the minimum threshold value is zero.
 7. The method according to claim 5, wherein the minimum threshold value is greater than zero.
 8. The method according to claim 1, wherein controlling the recirculation pump by varying the rotation speed of the recirculation pump comprises varying the rotation speed of the recirculation pump over the time according to a continuous function or a step function.
 9. The method according to claim 1, wherein the recirculation phase further comprises reestablishing the prefixed liquid level value inside the washing tub when the liquid level goes below the prefixed liquid level value by conveying an amount of water into the washing tub.
 10. The method according to claim 1, wherein the recirculation phase further comprises reestablishing the prefixed liquid level value inside the washing tub when the liquid level goes below the prefixed liquid level value by extracting an amount of water from the laundry in a dewatering process carried out by rotating the washing drum at a dewatering speed.
 11. The method according to claim 1, wherein the recirculation system comprises a second recirculation circuit configured to drain liquid from the bottom of the washing tub and to re-admit the liquid into a second region of the washing tub, wherein the variable speed recirculation pump is a bi-directional variable speed pump having a second outlet connected to the second recirculation circuit, and wherein varying the rotation speed of the recirculation pump during the recirculation phase comprises: activating the recirculation pump in a first direction of rotation to drain the liquid from the bottom of the washing tub and to re-admit the liquid into the first region of the washing tub through the recirculation circuit, and activating the recirculation pump in a second direction of rotation opposite to the first direction of rotation to drain liquid from the bottom of the washing tub and to re-admit the liquid into the second region of the washing tub through the second recirculation circuit.
 12. The method according to claim 11, wherein the recirculation pump is operated in the second direction at a first fixed speed.
 13. The method according to claim 11, wherein the recirculation pump is operated in the second direction at a speed varying over the time.
 14. The method according to claim 1, wherein the recirculation system comprises a second recirculation circuit configured to drain liquid from the bottom of the washing tub and to re-admit such liquid into a second region of the washing tub, wherein the outlet conveys liquid to a bifurcation for the recirculation circuit and the second recirculation circuit, wherein the recirculation circuits are configured so that a liquid in the second recirculation circuit requires a first pressure to reach the washing tub which is lower than a second pressure required for a liquid in the recirculation circuit to reach the washing tub, and in that the recirculation pump is operated at a first speed below, or equal to, a speed threshold to circulate liquid only in the second recirculation circuit to reach the washing tub and the recirculation pump is operated at a second speed above the speed threshold to circulate liquid both in the first recirculation circuit and the second recirculation circuit to reach the washing tub, wherein the step of controlling the recirculation pump by varying the rotation speed of the recirculation pump depending to the difference between the detected liquid level and the prefixed liquid level value is carried out when the recirculation pump is operated above the speed threshold.
 15. The method according to claim 14, wherein the recirculation pump is operated at a first speed to circulate liquid only in the second recirculation circuit to reach a bottom region of the washing tub and is operated at the second speed to circulate liquid also in the first recirculation circuit to reach an upper region of the washing tub. 